When overcurrent is generated in a path leading from a power source for a vehicle such as a hybrid vehicle or an electric vehicle to a load via a wire, the temperature of the wire becomes higher, and troubles might be generated such as smoke from an insulating coating or the like. Therefore, an overcurrent cutoff device that cuts off current is provided in case of overcurrent generation.
Conventionally, a fuse element is used in such an overcurrent cutoff device. However, a fuse melts at the time of overcurrent cutoff, and therefore, needs to be replaced with a new one. In view of this, an overcurrent cutoff device that does not use a fuse has been suggested to eliminate the trouble of maintenance or the like.
Patent Document 1 discloses an overcurrent cutoff device in which a PTC element is wound around a circuit conductor, and the PTC element is connected to a signal line. When overcurrent is applied to the circuit conductor, and the temperature of the circuit conductor becomes higher, the temperature of the PTC element also becomes higher. The resistance value in the PTC element then changes, and the voltage at both ends of the PTC element (the current flowing in the PTC element) changes. Based on the voltage (the current), the circuit is cut off, such that overcurrent generation is prevented.